Neonatal Fragment Crystallizable Receptor (FcRn)

The neonatal Fc receptor (FcRn) is a unique receptor responsible for regulating the homeostasis and transport of immunoglobulin G (IgG) and albumin. It protects IgG and albumin from lysosomal degradation, mediates transcytosis of IgG across cellular barriers, and plays a role in immune regulation and antigen presentation. FcRn is expressed in various tissues, including the placenta, endothelial cells, epithelial cells, dendritic cells, and macrophages. FcRn inhibitors are being developed as therapies for antibody-mediated diseases.

Other names

Neonatal Fc receptorFCGRT

FcRn binds monomeric IgGs/albumin inside acidified endosomes after cellular uptake via pinocytosis or receptor-mediated endocytosis. Bound ligands are recycled back to the cell surface where they are released into circulation due to loss of affinity at physiological pH. Unbound proteins are directed toward lysosomal degradation. In APCs, after internalization through classical activating/inhibitory Fcγ receptors, immune complexes containing antigens are sorted intracellularly by FcRn toward compartments that facilitate efficient cross-presentation—a process essential for robust adaptive immunity against pathogens or tumors.